1. Field of the Invention
The present invention relates to a timepiece comprising an annual or perpetual date display mechanism.
2. Description of Related Art
Known annual or perpetual date display mechanisms generally comprise an indication of the current month and the day of the week, in addition to the indication of the date. This information on the division of time, based on the period of rotation of the earth around the sun, is sometimes supplemented by information concerning the position of other celestial bodies, particularly the moon, with respect to the earth.
Although any annual or perpetual date mechanism necessarily comprises a month cam to determine the number of days in the month being displayed, none of these mechanisms has a display device for indicating the number of days in the month being displayed. However, this information is extremely useful in everyday life.
CH 538137 proposes a date mechanism indicating the days in the months. This mechanism is in fact a simple date mechanism in which the user, by moving a disc or a plate at any time during the month, sets the mechanism to skip from the last days of the month to the 1st of the next month. It therefore makes the correction before and not afterwards. This is why the number of days in the month is indicated. It enables the user to know whether the mechanism is in the correct position for changing from the 28th, 29th, 30th or 31st to the 1st of the next month. The purpose is therefore not to indicate the number of days in the month, but to show whether the date mechanism has been set to the correct position. In the case of this mechanism, therefore, the number of days in the month has to be indicated by the user; the mechanism does not do this automatically. In fact, since the correction is made manually and can be made at any time during the current month, the indicated number 28, 29, 30 or 31 does not mean that the month has the number of days indicated, since the change is not automatic. By contrast with conventional simple date mechanisms in which the user has to change the date five times per year, in this case he has to change it ten times per year, since he also has to move the disc from 30 to 31 days, failing which the date mechanism will skip the 31st day of the 31-day month following a 30-day month, whereas in a simple date mechanism the 31st is always indicated by default and therefore requires no correction.